661365 has 40 divisors (see below), whose sum is σ = 1254528. Its totient is φ = 332640.

The previous prime is 661361. The next prime is 661373. The reversal of 661365 is 563166.

It is not a de Polignac number, because 661365 - 2² = 661361 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

661365 is a lucky number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 661365.

It is not an unprimeable number, because it can be changed into a prime (661361) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 9280 + ... + 9350.

2⁶⁶¹³⁶⁵ is an apocalyptic number.

It is an amenable number.

661365 is a deficient number, since it is larger than the sum of its proper divisors (593163).

661365 is a wasteful number, since it uses less digits than its factorization.

661365 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 111 (or 102 counting only the distinct ones).

The product of its digits is 3240, while the sum is 27.

The square root of 661365 is about 813.2435059685. The cubic root of 661365 is about 87.1258582678.

It can be divided in two parts, 66 and 1365, that added together give a triangular number (1431 = T₅₃).

The spelling of 661365 in words is "six hundred sixty-one thousand, three hundred sixty-five".